The Off-Grid Home

Eco ex­pert Tim Pullen ex­plains what to con­sider when build­ing a home away from mains ser­vices

Homebuilding & Renovating - - CONTENTS -

Im­ages: sI­mon max­well

Awalk, per­haps some half a mile from the road along a track through a pretty blue­bell wood, leads to a big clear­ing. A gen­tle, south-fac­ing slope me­an­ders down to a lake where there are ducks glid­ing across its shim­mer­ing top, moorhens fos­sick­ing around the mar­gins and fish frol­ick­ing be­neath the sur­face. In this case, it is the fish that will make a busi­ness ven­ture pos­si­ble and that will en­able plan­ning con­sent to be granted for a new house.

A dream sce­nario made real. But, there’s a prob­lem — there’s no pos­si­bil­ity of ac­cess to any mains ser­vices. If this house is to be built, it has to be built en­tirely off-grid.

This sit­u­a­tion does come up, al­beit rarely. Plan­ning con­sent ob­tained in a re­mote lo­ca­tion, that en­ables a house to be built to sup­port a ru­ral busi­ness ven­ture. There are other self-builders that build in less re­mote lo­ca­tions but sim­ply choose to be off-grid. In either case the chal­lenges re­main the same: the de­vel­op­ment has to pro­duce its own heat and power, deal with its own waste and pro­vide its own wa­ter. And, fi­nally, there are many in ru­ral lo­ca­tions who may be off-grid for some pro­vi­sions (i.e. mains gas and mains drainage), but not all (say, elec­tric­ity and wa­ter); the self-builder or ren­o­va­tor will still need to put some con­sid­er­a­tion into how these pro­vi­sions will be made.

it all starts with de­sign

Mark Waghorn, owner and direc­tor of Mark Waghorn De­sign, is an ar­chi­tect spe­cial­is­ing in low­im­pact, sus­tain­able house de­sign. “Keep it sim­ple,” he be­gins. “The tra­di­tional house form (i.e. akin to what a child would draw) has a lot go­ing for it. It is easy to build and has a low sur­face area to vol­ume ra­tio, which helps with heat re­ten­tion.”

The wis­dom of these words can be seen in his in­no­va­tory, award-win­ning de­signs which are low-im­pact, with low en­ergy con­sump­tion and are rel­a­tively cheap to build. All of which are key is­sues for the off-grid house.

By far the largest en­ergy use in a typ­i­cal house is in space heat­ing, but it does not need to be that way. As Mark says: “If you are off-grid, there is an even greater im­per­a­tive to min­imise your heat­ing re­quire­ment. If you build to the Pas­sivhaus stan­dard, for in­stance, the need for any space heat­ing will be next to zero.”

But this as­sumes that there is some dif­fi­culty in gen­er­at­ing heat en­ergy. An off-grid house will be re­liant on the site’s re­sources for en­ergy, wa­ter and waste man­age­ment, as a min­i­mum. I know of an off-grid home in mid-Wales, set in the mid­dle of a

70-acre wood­land where the own­ers live and work on their land. Their house is not par­tic­u­larly en­ergy ef­fi­cient, but they do have ac­cess to more wood than they can ever con­sume in heat­ing the house.

Con­sid­er­ing your life­style be­fore you plan is par­tic­u­larly key to the off-grid home. Think about the ap­pli­ances you use and your daily rou­tine and fac­tor this into your de­sign to keep con­sump­tion low. “Think about the type and ar­range­ment of an­cil­lary, ex­ter­nal ac­com­mo­da­tion,” adds Mark. “Glazed spa­ces at­tached to the house can be use­ful for a mul­ti­tude of dif­fer­ent func­tions — dry­ing clothes, grow­ing food or sea­sonal ex­pan­sion of liv­ing ac­com­mo­da­tion.” In a low-en­ergy, off-grid home, an­cil­lary space can also pro­vide boot­rooms, larders and biomass stores at a very low build cost, with al­most zero en­ergy de­mand.

gen­er­at­ing en­ergy

There are two is­sues to con­sider: min­imis­ing the en­ergy de­mand in the first in­stance and know­ing ex­actly what that de­mand will be, as it changes day-to-day and sea­son-to-sea­son. Off-grid means ex­actly that; it is not on the grid and there is no back-up. It means that the site has to pro­duce all it needs but, ideally not more than is needed as the sur­plus will just be wasted (un­less there is pro­vi­sion for en­ergy stor­age, which we’ll come back to later).

The so­lu­tion starts with the most ac­cu­rate pos­si­ble cal­cu­la­tion of the en­ergy de­mands, di­vided into space heat­ing, hot wa­ter and elec­tric­ity. In­dus­try stan­dards sug­gest roughly 1,000kWh/ yr per per­son liv­ing in the house for hot wa­ter and 1,500kWh/yr per per­son for elec­tric­ity. The space heat­ing de­mand will vary with the size and con­struc­tion of the house but Build­ing Reg­u­la­tions set out a max­i­mum per­mit­ted of 55kWh/m2/yr.

Space heat­ing and hot wa­ter (and cook­ing) could be pro­duced us­ing bot­tled gas. It is in­ef­fi­cient, ex­pen­sive and some dis­tance from sus­tain­able, but it is flex­i­ble and pre­dictable. This could also be achieved with biomass (har­vested or bought-in log pel­lets) which would be cheaper, more ef­fi­cient and sus­tain­able. Al­ter­na­tively, it might be that heat­ing is to be pro­duced us­ing elec­tric­ity —➤prob­a­bly via a

“An off-grid house will be re­liant on the site’s re­sources for en­ergy, wa­ter and waste man­age­ment”

heat pump. That means gen­er­at­ing more elec­tric­ity and in­vest­ing more in gen­er­a­tion and stor­age tech­nol­ogy.

There are two truths that have to be recog­nised:

l Hit­ting ex­actly 100% of de­mand is prac­ti­cally im­pos­si­ble. What is wanted and what is be­ing pro­duced will both vary with the cir­cum­stances on any given day and as a re­sult there will al­ways be a sur­plus or a short­fall.

l There is no elec­tric­ity-gen­er­at­ing tech­nol­ogy that gives pre­dictable pro­duc­tion, day-to-day and sea­son-to-sea­son. We can pre­dict with some ac­cu­racy what any tech­nol­ogy will pro­duce over the course of a year. But, as the tech­nolo­gies cur­rently avail­able at the do­mes­tic level are re­liant on the weather, we can’t pre­dict what it will pro­duce on any given day.

What this leads to is the need for en­ergy stor­age and, prob­a­bly, an­other tech­nol­ogy for back-up. Although, not al­ways — if the heat en­ergy is, for ex­am­ple, pro­duced from biomass then stor­age is a non-is­sue. Elec­tric­ity stor­age, how­ever, means a bat­tery bank, which leads to an­other cal­cu­la­tion — how big does the bat­tery bank need to be? If a pho­to­voltaic (PV) so­lar sys­tem is the prin­ci­pal means of gen­er­at­ing elec­tric­ity, it’s worth know­ing that the in­dus­try sets out that broadly 50% of the an­nual pro­duc­tion will be in the three sum­mer months and only 10% in the three win­ter months. So, do you want to store that sum­mer sur­plus un­til win­ter – that will need a prodi­giously big bat­tery bank – or have a se­cond tech­nol­ogy, wind, say, that works bet­ter in win­ter?

This leads to yet an­other cal­cu­la­tion. As an ex­am­ple: one day could be grey and over­cast with no wind. An­other day could see bright sun­shine with plenty of wind. Easy-peasy to store a fair­weather, sunny day’s sur­plus to keep you go­ing on greyer days. But how long will grey con­di­tions go on for and how big does the bat­tery have to be?

A 5kW wind tur­bine will pro­duce around 9,000kWh and a 10kW PV sys­tem will pro­duce about 8,500kWh per year. A 1kW hy­dro-power scheme will pro­duce around 8,000kWh per year. It will still be af­fected by the weather (more rain equals more pro­duc­tion) but is far more re­li­able, and pre­dictable, than other tech­nolo­gies. All of these sys­tems pro­duce more than enough to sat­isfy the de­mands of the house. But all will pro­duce a sur­plus at some time of the year and a short­fall at oth­ers. A com­bi­na­tion of tech­nolo­gies – say a 5kW PV with a 3kW wind tur­bine and a small bat­tery bank – is re­ally the only way to be sure.

“All tech­nolo­gies cur­rently avail­able at the do­mes­tic level are re­liant on the weather so we can’t pre­dict what it will pro­duce on any given day”

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.